ML18038B139

LER 95-001-00:on 950123,DG Turbocharger Failed & Resulted in Noncompliance W/Ts Lco.Performed Failure Analysis on Turbocharger

ML18038B139
Person / Time
Site:	Browns Ferry
Issue date:	02/22/1995
From:	Austin S TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18038B138	List: ML18038B137 ML18038B139
References
LER-95-001-01, LER-95-1-1, NUDOCS 9503010224
Download: ML18038B139 (14)

Text

NRC rORM 366 U S IRICLEAR REGULATORY C(NNIISS I ON APPROVED SY (NNI NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE . TO CNIPLY IIITH THIS INFORHATION COLLECTION REQUEST: 50.0 NRS.

LZCENSEE EVENT REPORT (LER) FORNARO COHMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION ANO RECORDS MANAGEHENT BRANCH (HNBB 7714), U.S. NUCLEAR REGULATORY COMHISSIOH ~

NASHINGTON, DC,20555-0001 AND TO THE PAPERNORK REDUCTION PROJECT (3140-0104), OFFICE OF HANAGEHENT AND 'BUDGET UASHINGTON DC 20503.

FACILITY NAME (1) DOCKET IRMKR (2) PAGE (3)

Browne Ferry Nuclear Plant (BFN) Unit 2 05000260 1OF7 TITLE (4) Diesel Generator Turbocharger Failure That Resulted In Noncompliance With Technical Specification Limiting Condition For 'Operation EVENT DATE 5 REPORT DATE 7 OTHER FACILITIES INVOLVED 0 SEQUENTIAL REVISION FACILITY NAHE DOCKET NUMBER HOHTH DAY YEAR YEAR HOHTH DAY YEAR NA NUMBER NUHBER FACILITY NAME DOCKET NUMBER 01 23 95 95 001 00 02 22 NA OPERATING THIS REPIXIT IS SIÃNITTED PlÃSUANT TO THE RHRIIRH%3ITS OF 10 CFR = Cheek onc or morc IRX)E (9) 20.402(b) 20.405(c) 50.73(a)(2)(iv) 73.71(b)

POUER 20.405(a)(1)(i) 50.36(c)(1) 50 '3(a)(2)(v) 73.71(c)

LEVEL (10) 100 20.405(a)(1)(ii) 50.36(c)(2) 50.73(a)(2)(vii) OTHER 20.405(a)(1)(iii) 50.73(a)(2)(i) 50.73(a)(2)(viii)(A) 20.405(a)(1)(iv) 50.73(a)(2)(ii) 50.73(a)(2)(viii)(B) 20.405(a)(1)(v) 50.73(a)(2)(iii) 50.73(a)(2)(x)

LICENSEE C(NTACT FOR THIS LER 12 NAHE TELEPHONE NUHBER (Include Area Code)

Steven W Austin, Compliance Licensing Engineer (205)729-2070 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBE D IN THIS REPORT 13 SYS REPORTABLE REPORTABLE CAUSE COMPONENT MANUFACTURER CAUSE SYSTEM COHPONENT MANUFACTURER TEH TO NPRDS TO NPRDS EK TUR M494 N SUPPLEMENTAL REPORT EXPECTED 14 EXPECTED MONTH DAY YEAR YES SlaM I SSI ON g (If yes, carplete EXPECTED SUBMISSION DATE). ,DATE (15) 04 28 95 ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typeNritten lines) (16)

On January 23, 1995 at 2005 hours0.0232 days <br />0.557 hours <br />0.00332 weeks <br />7.629025e-4 months <br />, TVA exceeded the Limiting Condition for Operation (LCO) for an inoperable Emergency Diesel Generator (EDG). At 2005 hours0.0232 days <br />0.557 hours <br />0.00332 weeks <br />7.629025e-4 months <br />, on January 16, 1995, following approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> of operation, EDG C .was declared inoperable when it failed to go through the proper shutdown sequence after a stop signal was initiated. The EDG was returned to operable status on January 25, 1995 at 1330 hours0.0154 days <br />0.369 hours <br />0.0022 weeks <br />5.06065e-4 months <br />. Failure of the turbocharger planetary gear tra'in initiated the event. The planetary gears supply the motive force for the turbocharger for engine loads less than 70 percent. At loads greater than 70 percent the exhaust gases provide the motive force for the turbocharger. During the event, as the engine was unloaded, the amount of available exhaust gas decreased to where the turbocharger would have been driven from the planetary gears. However, because the gears had failed, the turbocharger did not supply combustion air, and the engine shutdown. The EDG was repaired and returned to service. Zn order to attempt to determine. the root cause of the event@ TVA is performing a failure analysis on the turbocharger. TVA's reporting this event in accordance with 10 CFR 50.73(a)(2)(i)(B), as any operation or condition prohibited by the plant's Technical Specifications.

9503010224 950222 PDR ADOCK 05000260 S PDR NRC FORH 366 (5-92)

4>

NRC FORH 366A U-S- IN)CLEAR REGULAT(XIY CQBIISSI(NI 'APPROVED BY (%% NO- 3150-0104 (5-92) EXPIRES '/31/95 ESTIHATED BURDEN PER RESPONSE 'TO CDHPLY lJITH THIS INFORHATIOH COLLECTION REQUEST: 50.0 HRS. FORNARD CDHHENTS REGARDING BURDEN EST IHATE TO THE INFORHATION AND RECORDS HANAGEKENT BRANCH (HNBB 7714), U.ST NUCLEAR REGULATORY CDHNISSIOH,

'LICENSEE EVENT REPORT NASHINGTON, DC 20555-0001, AND TO THE PAPERNORK REDUCTION TEXT CONTINUATION PROJECT (3150-0104), OFFICE OF HANAGEHENT AND BUDGET, UASHINGTON DC 20503 FACILITY NHK (1) DOCKET IRaJI (2) LER ImKR (6) PAGE (3)

YEAR SEQUENTIAL REVISION NUHBER 'NUHBER Browns Ferry Unit 2 05000260 95 001 ,00 2 of 7 TEXT If more s ce is r ired use additional co ies of NRC Form 366A (17)

PLANT CONDITIONS Unit 2 was in the run mode at 100 percent power or 3293 megawatts thermal. Units 1 and 3 were .shutdown and defueled.

'n January 16, 1995 at approximately 1535 hours0.0178 days <br />0.426 hours <br />0.00254 weeks <br />5.840675e-4 months <br />, operations

.commenced the Diesel Generator C Monthly Operablilty Test. This test is performed to determine the operability of the Emergency Diesel Generator (EDG)[EK].

ZZo DESCRIPTION OF EVENT A. Events On January 23, 1995, at 2005 hours0.0232 days <br />0.557 hours <br />0.00332 weeks <br />7.629025e-4 months <br />, TVA .exceeded the Limiting Condition for Operation (LCO) for an inoperable EDG. This resulted in Unit 2 being in a condition prohibited by the plants Technical Specifications (TS). The details which led to this event are provided below.

On January 16, 1995, at 2005 hours0.0232 days <br />0.557 hours <br />0.00332 weeks <br />7.629025e-4 months <br /> following approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> of operation, the EDG C was unloaded and given a stop signal. When a stop signal is initiated, the EDG is designed to decelerate from full speed (900 revolutions per minute (RPM)) to idle speed (450 RPM) and sustain the idle speed for approximately 11.5 minutes then stop. This is necessary to allow the engine, especially turbocharger bearings, to cool. However, when the stop signal was given, the engine decelerated to approximately 150 RPM and shutdown.

Thus, TVA declared EDG C inoperable and entered a 7 day LCO for an inoperable EDG. BFN Unit 2 Technical Specifications (TS) state that, when one of the Units 1 and 2 Diesel Generator is inoperable, continued reactor power operation is permissible during the next 7 days provided 2 offsite power sources are available and all Core Spray (CS) [BM], Residual Heat Removal (RHR) [BO] (Low Pressure Coolant Injection and Containment Cooling) systems and the remaining Units 1 and 2 Diesel Generators are operable. If this requirement cannot be met, the reactor shall be in cold shutdown condition in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

Due to the time involved in obtaining the necessary parts and making the repairs, TVA was unable to return the EDG to operable status within the required LCO time limit. Thus, on January 23, at 2005 hours0.0232 days <br />0.557 hours <br />0.00332 weeks <br />7.629025e-4 months <br />, TVA exceeded the 7 day LCO for the '995, inoperable. EDG. Prior to the LCO time limit expiring, TVA

h )

NRC FQN 366A (5-92)

U '. IN)CLEAR REGULATORY CQBIISSIQI APPROVED BY QBI NO. 3150-0104 EXPIRES 5/31/95 ESTINATED BURDEN PER RESPONSE TO CONPLY NITH THIS INFORNATION COLLECTIOH REQUEST: 50.0 HRS. FORNARD CQWENTS REGARDING BURDEN EST INATE TO THE INFORNATION AND RECORDS NANAGENENT BRANCH '(NNBB 7714) ~ U.S. NUCLEAR REGULATORY CONNISSION, LICENSEE EVENT REPORT NASHINGTON, DC 20555-0001, AND TO THE PAPERNORK REDUCTION TEXT CONTINUATION :PROJECT (3150-0104), OFFICE OF HANAGENENT AND BUDGET, NASHINGTON DC 20503 FACILITY KAID (1) DOCXEl'RBCKR (2) LER'IRBRER (6) PAGE (3)

YEAR SEQUENTIAL REVI S I OH

'NUHBER NUNBER Browns Ferry Unit 2 05000260 95 001 00 3 of 7 TEXT If more s ce is r ired use additional co les of NRC Form.366A (17) requested and received'iscretionary Enforcement from the requirements of the TS. TVA received permission to continue reactor power operation for an additional 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> while the repairs were being, made to the EDG.

On January 25, 1995 at 1330 hours0.0154 days <br />0.369 hours <br />0.0022 weeks <br />5.06065e-4 months <br />, after completing the necessary repairs .and passing the required post maintenance testing, EDG C was declared operable and the .established LCO was exited.

This event is reportable in accordance with 10 CFR 50.73.(a)(2)(i)(B), as any operation of condition prohibited by the, plant's Technical Specifications.

- Ino erable Structures Com nents or S stems that Contributed to the Eventl None.

C, Dates and A roximate Times of Ma or Occurrencest January 16, 1995, at 2005 CST Emergency Diesel Generator C is declared inoperable. TVA subsequently enters a 7 day LCO.

January 23, 1995, at 2005 CST TVA exceeds the 7 day LCO for an inoperable, EDG. Previously that day, TVA requested and received Discretionary Enforcement from the requirements of the LCO.

January 25, 1995, at 1330 CST Repairs were completed and the EDG C is declared operable.

The LCO for an inoperable EDG is exited.

D. Other S stems or Seconda Functions Affected:

None.

E, Method of Discove Personnel in..the EDG room witnessed the, failure of the EDG to properly shutdown.

NRC FORH 366A U.S INCLEAR REGULATORY CQBIISSIM APPROVED BY (HEI HO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPONSE TO CDHPLY lllTH THIS INFDRHATIDN COLLECTIDH REQUEST: 50.0 BR'DRIIARD COHHEHTS REGARDING BURDEN ESTIHATE TO THE INFDRHATION AND RECORDS liANAGEHENT BRANCH '(HNBB 7714), U.S. NUCLEAR REGULATORY COHHISSIDN, LZCENSEE EVENT REPORT MASHINGTOH, DC 20555-0001, AND TO THE PAPERHORK REDUCTIOH TEXT 'CONTZNUATZON PROJECT (3150-0104), OFFICE OF HANAGEHENT AND 'JRSGET, llASHINGTDH DC 20503 FACILITY IWK (1) DOCKET IRHIKR C2) LER IRMKR C6) PAGE C3)

YEAR SEGUENTIAL REVI SIOH NUHBER NUIIBER Browns Perry Unit '2 05000260 95 001 00 4 of 7 TEXT If more s ce is r ired use additional co les of NRC Form 366A (17)

F~ erator Actionst None.

0 Safet S stem Res nsesI None.

ZZZ. CAUSE OF THE EVENT A. Zmmediate Cause:

The immediate cause of the event,was the failure of the turbocharger which resulted in a failure of the EDG to go through the shutdown sequence.

Root Cause:

This event resulted from a failure of the turbocharger planetary gear train. Zn order to determine the root cause for this event, TVA is conducting a failure analysis of the turbocharger.

The turbocharger is driven by a connecting gear train which drives the turbocharger during starting, and light load (less than 70 percent load) conditions. Under these conditions, there is not enough energy in the exhaust gases to drive the turbocharger. When the engine reaches approximately 70 percent load, exhaust gas energy will drive the turbocharger faster than the gear train. Then the turbocharger will'isengage itself from the gear train and be driven by the exhaust gases.

During the event, as the engine was unloaded and the amount of available exhaust gases decreased, the turbocharger decelerated to a point where it should have been driven from the planetary gear train. The decrease in the exhaust gas resulted in a removal of the driving force to the turbocharger. Because the gear train had failed, combustion air was lost. At this point, the engine shutdown.

During the operability test, the EDG performed as designed. Up to the time the shutdown sequence was initiated, the personnel involved had .no indication that the turbocharger failure was about to occur.

The turbocharger has been in service since 1986. The EDGs were

.updated, replacing the turbochargers with high capacity units.

TVA has been trending EDG reliability data since mid-1987. The turbocharger for EDG C failed after over 157 starts.

Additional'ly, TVA's maintenance program follows guidance provided'

4l II I~

NRC FCXN 366A U S IN)CLEAR REGULATORY CCNHII SSICHI APPROVED BY QHI NO 3150-0104 (5-92) EXPIRES '/31/95 ESTIHATED BURDEN PER RESPONSE TO COHPLY lJITH THIS INFORHATIOH COLLECTION RE(NEST I 50. 0 HRS. FORlJARD COHHENTS REGARD IHG BURDEN EST II(ATE TO THE INFORHATION AND RECORDS HANAGEHENT BRANCH '(HHBB 7714), U.S. NUCLEAR REGULATORY C(NHISSI ON, LICENSEE EVENT REPORT NASHINGTOH, DC 20555-0001 ~ AHD TO THE PAPERlJORK REDUCTION TEXT CONTINUATION PROJECT (3150-0104), OFFICE OF HANAGEHENT AND BUDGET, lJASHINGTON DC 20503 FACILITY WUK (1) DOCKET IRHRIER C2) LER IkHRKR C6) PAGE C3)

YEAR SEQUENTIAL REVI SI OH HUNGER NUHBER

,Browns Ferry Unit 2 05000260 95 001 00 5 of 7 TEXT If more s ce is r ired Use edditionet co les of NRC Form 366A (1)')

by the vendor. Therefore, it is highly unlikely that the failure could be attributed to age or improper maintenance.

,In addition to the, turbocharger replacement, TVA replaced the engine stub shaft assembly with'one of a revised design However, after the installation, it was determined that the revised stub shaft assembly's oil chamber did not completely match the diesel engine block and the stub shaft assembly would have to be replaced. The stub shaft assembly that was on the engine at the time of the turbocharger failure was refurbished and returned to service.

C. Contzibutin Factorst None.

IV, ANALYSIS OF THE EVENT The EDGs are. part of the standby AC power system that provides a highly reliable source of power as required for Emergency Core Cooling Systems. The EDGs ensure no single credible event can disable the core stand by cooling functions of their supporting activities.

Emergency Diesel Generator C supplies emergency power to RHR pump 2Bg CS Pump 2B, RHR Service Water Pump B2 fBI], and Emergency Equipment Cooling Water Pump B3 .(BI].

BFN is analyzed for a 7 day allowed outage time (AOT), during which no single failure is assumed to occur in conjunction with a Design Basis Accident. TVA requested Discretionary Enforcement that extended the AOT an additional 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. During that timey standby auxiliary power for the, above equipment was not available from its normal EDG. The three remaining RHR and CS pumps were powered from both the normal offsite power source and, if required, their normal EDGs. For long term loss of offsite power, EDG 3C could have been manually aligned through existing board tie breakers to supply power to the equipment normally powered by EDG C.

The failure of the EDG turbocharger was discovered during the unloading and shutdown sequence of the EDG. The failure became self-evident upon unloading of the EDG. Because the EDG operated as designed up to the time when the turbocharger failure occurred, this event did not affect the safety of the plant, its personnel, or the public.

4l 4l J NRC F(NOI 366A U S. IRICLEAR REGULATORY C(NBIISSI(NI APPROVED BY (NRI NO. 3150-0104 (5-92) EXPIRES 5/31/95 ESTIHATED BURDEN PER RESPONSE TO CONPLY WITH THIS IHFORHATIOH COLLECT ION REQUEST: 50.0 HRS. FORNARD COHNEHTS REGARDING BURDEN EST IHATE TO THE IHFORHATIOH AND RECORDS HAHAGEHEHT BRANCH (NNBB 7714), U.S. NUCLEAR REGULATORY COHHISSIOH, LICENSEE EVENT REPORT llASHIHGTDH, DC 20555-0001, AND TO THE PAPERMORK REDUCTION TEXT CONTINUATION PROJECT (3150-0104) ~ OFFICE OF HANAGEHEHT AND BUDGETg WASHINGTON DC. 20503 FACILITY Nba (1) DOCKET IRB%ER (2) LER IRNSER (6) PAGE (3)

YEAR,. SEQUENTIAL REVISION NUNBER NUHBER Browns Ferry Unit 2 05000260 95 001 00 6 of 7 TEXT If more s ce is r ired use eddf ons c ies of NRC Form 366A (17)

Vo CORRECTZVE ACTIONS A. Immediate Corrective Actionsi Emergency Diesel Generator C was placed under .an administrative hold and secured so it could not be started.

The turbocharger on the EDG was replaced. After completing post maintenance testing, the EDG was returned to standby readiness.

B. Corrective Actions to Prevent Recurrence:

The turbocharger was sent offsite and disassembled for a failure analysis. Prel'iminary results are currently being evaluated.

TVA will provide -a supplemental report following the completion of the failure analysis.

VZ. ADDITIONAL ZNFORMILTZON A Failed Cpm onents:

The failed planetary gear train is part of a model 9526867 turbocharger from Power Systems Division of Morrison-Kudsen, supplied as part of a Model 999-20 General Motors stationary power generating plant.

Bo Previous LERs on Similar Events:

There have: been no previous LERs issued where an EDG could not be returned to service during the 7 day LCO time limit. However, on two recent occasions, TVA experienced a turbocharger failure on one of the EDGs.

On October 17, 1984, EDG 3A experienced a failure with one of the original capacity turbochargers. In this instance, the turbocharger itself experienced a failure. TVA believed the cause of this failure to be failure of the compressor bearing assembly. The turbocharger was replaced and the EDG was returned to service on October 21, 1984, within the allowed LCO time limit.

On August 25, 1992, EDG 3A experienced a failure of one of the high capacity turbochargers. TVA's investigation found that the planetary gear set and the sun gear failed, initiating the event.

The turbocharger was shipped to General Motors for failure analysis. They determined that the cause of the failure was planetary bearing failure, which caused a loss of concentricity within the gear train. The loss of concentricity within the gear train resulted in an improper meshing of the associated gear

~i I J

'v jI

~k>

NRC FORJI 366A U.S. IRJCLEAR REGULAT(XIY. CQHII SSI ON APPROVED'Y (WI NO'150-0104 (5-92) EXPIRES 5/31/95 ESTINATED BURDEN PER RESPONSE TO CONPLY IJITH THIS INFORNATION COLLECTION REOUEST: 50.0 NRS. FORIJARD 'CONNEHl'S REGARDING BURDEN EST I JIATE TO THE IHFORNATION AND RECORDS JIAHAGENENT BRANCH (NNBB 7714), U.S. NUCLEAR REGULATORY CONMI SS I OH, LICENSEE EVENT REPORT MASHIHGTOH, DC 20555-0001 ~ AND TO THE PAPERIJDRK REDUCTION TEXT CONTZNUATZON PROJECT. (3150-0104), OFFICE OF NANAGENENT AND BUDGET@

IJASHINGTOH 'DC 20503 FACILITY IOUS -(1) DOCKET IRMKR (2) LER IRINJER (6) PAGE (3)

YEAR SECHJEHT IAL REVI SION NUNBER NUNBER Browns Ferry Unit 2 05000260 95 001 00 7 of 7 TEXT If more s ce is r ired use.additional co ies of NRC Form 366A (1/)

teeth. The root cause of the bearing failure was not possible to determine, but similar failures have occurred at other utilities due to improper lubrication. However, during disassembly of EDG C, lubricating oil was evident on all bearing surfaces and all drilled oil passages appeared to be clear. The EDG 3A was returned to .service on September 1, 1992, within the LCO time limit.

VZZ ~ Commitments:

The actions described in section V of this, report are not Regulatory

.Commitments. That is, they are not actions required to restore compliance with obligations. Obligations means an action that is a legally binding requirement imposed through applicable rules, regulations, orders, and licenses. The actions being taken are to further determine the cause of the event.

brackets' Energy Zndustry .Identification System (EZZS) system and component codes are identified in the text with (e.g., (XX)).

II 1